1. Field of the Invention
This invention is concerned with synthesis of crystalline aluminosilicate zeolites.
2. Description of the Prior Art
A number of synthetic crystalline zeolites have previously been prepared. They are distinguishable from each other and from naturally occurring zeolites on the basis of composition, crystal structure and sorptive properties. The existence of a number of zeolites having similar but distinguishable properties advantageously permits the selection of a particular member having optimum properties for a particular use.
Such synthetic crystalline aluminosilicates are ordinarily prepared initially in the alkali metal form of the crystal; the process of preparation involving heating, in aqueous solution, of an appropriate mixture of oxides, or of materials whose chemical composition can be completely represented as a mixture of oxides: alkali metal oxide, silica, alumina and water, at a temperature of approximately 100.degree. C. for a period of from 15 minutes to 90 hours or more. The product which crystallizes within this hot mixture is separated therefrom and water washed. The aluminosilicate may then be activated by heating until dehydration is attained. It has also heretofore been known to synthesize zeolites from systems containing quaternary ammonium ion, in particular, the tetramethylammonium (TMA) cation. Other types of organic bases have been employed including tetraethylammonium (TEA) and large cations derived from 1,4-diazabicyclo - (2.2.2.) octane. The latter are particularly described in U.S. Pat. No. 3,459,676 dealing with synthesis of zeolite ZK-20. Representative of zeolites crystallized from a reaction mixture containing tetramethylammonium cations is ZK-4 described in U.S. Pat. No. 3,314,752. Crystalline aluminosilicate zeolite, of course, consist of a three-dimensional lattice formed of AlO.sub.4 and SiO.sub.4 tetrahedra cross-linked by the sharing of oxygen atoms, the negative charge on the AlO.sub.4 tetrahedra being balanced by the inclusion in the lattice of cationic charge equivalent to that on the lattice aluminum.